Comparison of 30- and 50-mCi Doses of Iodine-131 for Thyroid Ablation

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Abstract
The utility of lower (30 mCi) and higher (50-60 mCi) doses of 131I used to ablate residual thyroid tissue after thyroidectomy for carcinoma was compared. Whole body scans were done using 1 mCi 131I, 3 wk after withdrawal of triiodothyronine. Patients had received ablation therapy within 3 days after scanning, and 1 or more subsequent scans were analyzed. Patients (48) were treated to ablate residual thyroid tissue that was presumed to be normal. Among 18 patients given the lower dose of 131I as outpatients, 15 had successful ablation and 3 needed a 2nd administration; all 30 patients treated with the higher dose had successful ablation. Seventeen additional patients, presumed to have residual cancer, received 50-150 mCi; and 6 needed treatment. Although 1 dose of 50-60 mCi 131I provides more certain ablation, use of the usually effective 30 mCi dose for initial ablation is justified by the convenience of outpatient administration, the lower expense and the lower whole-body radiation dose.